Phosphorus fixation capacity of CaO-SiO2-Al2O3-MnO-Ce2O3 slag based on structural considerations*

The phosphorus fixation capacity of some slag systems, such as Ce2O3-containing slag, has hardly been investigated from a thermodynamics view due to the lack of relevant thermodynamic data. Since the macroscopic properties are primarily determined by the microscopic structure, the correlation between phosphorus fixation capacity and slag structure was explored by spectroscopy (XPS), Raman spectroscopy, and ferromanganese dephosphorization experiments. The results show that the predominant species of P5+ are Q0P (PO34 ) and Q1P (P2O47 ) units in the CaO-SiO2-Al2O3-MnO-Ce2O3-P2O5 quenched slag, and the phosphorus fixation capacity increases with the Q1P (P2O4-7) unit to Q0P (PO34 ) unit transformation (the P-O0 bond to P-O- bond transformation) since the electron cloud density between P and O atoms increases and the average radius of P-O bonds decreases. Especially, CaO or Ce2O3 as a network modifier can release the O2- and promote the P-O0 bond to P-O- bond (connected to Ca2+/Ce3+) transformation in the quenched slag. Furthermore, the phosphorus enrichment phases in the slow cooling slag are confirmed as nCa2SiO3-Ca3P2O8 (nC2S-C3P) and CePO4 solid solutions by the scan electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive spectrometer (EDS) methods. The results show Ce2O3 can depolymerize the polyphosphate structure partially replacing CaO after introducing Ce2O3 into CaO based slag because of its strong ability to donate electrons. The above results not only help to understand the dependence of phosphorus fixation capacity on slag composition from a structural view, but also provide the theoretical guidance for optimizing the composition of Ce2O3-containing dephosphorization slag. (c) 2022 Chinese Society of Rare Earths. Published by Elsevier B.V. All rights reserved.